Mechanism for changing rate of automatic fire



31, 1967 F. E. STURTEVANT 3,301,133

MECHANISM FOR CHANGING RATE OF AUTOMATIC FIRE Filed Jan. 21, 1965 2 Sheets-Sheet 1 IN VEN TOR. FOSTER E. STURTEVANT ATTORNEYS Jan. 31, 1967 F. E. STURTEVANT 3,301,133

MECHANISM FOR CHANGING RATE OF AUTOMATIC FIRE Filed Jan. 21, 1965 2 Sheets-Sheet 2 IN VENTOR. FOSTER E. STURTEVANT WW M? ATTORNEYS United States Patent 3,301,133 MECHANISM FOR CHANGING RATE OF AUTOMATIC FIRE Foster E. Sturtevant, West Hartford, Conn, assignor to Colts 1110., Hartford, Conn., a corporation of Arizona Filed Jan. 21, 1965, Ser. No. 426,737 14 Claims. (Cl. 89-131) The present invention relates to an automatic firearm and more particularly to a new and improved firing rate control device for firearms wherein the automatic operation thereof is controlled by the bolt and its related parts.

It is a principal object of the present invention to provide a firearm capable of automatically controlling and retarding the rate of fire or speed at which the firearm is discharged during automatic operation.

Another object of the present invention is to provide an automatic firearm adapted to exhibit a delayed automatic firing operation without requiring substantial correction or alteration in the lockwork or other working mechanisms of the firearm.

A further object of the present invention is to provide a firearm which can be changed from a normal automatic firing speed to a slow speed in a rapid, smooth and facile manner.

A still further object of the present invention is to provide a totally enclosed firing rate control device for an automatic firearm capable of effectuating with case a change in the speed of automatic operation while not effecting semiautomatic or single shot operation of the firearm.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawings:

FIG. 1 is a side view partly in section and partly broken away showing portions of the firing control mechanism embodying the present invention, the phantom line portions illustrating the firearm in a cocked position prior to firing and the full line portions illustrating an intermediate stage of automatic operation of the firearm.

FIG. 2 is an enlarged sectional view similar to FIG. 1 showing a similar fire control device immediately prior to release of the hammer during automatic operation.

FIG. 3 shows the device of FIG. 2 with portions of the assembly in a difl'erent relative arrangement after release of the hammer.

FIG. 4 is an enlarge-d sectional view similar to FIG. 3 showing a modified construction of the firing control device of the present invention.

Referring now to the drawings in greater detail wherein like reference characters indicate like parts throughout the several figures, there is shown a firearm adapted for automatic and semiautomatic operation. For purposes of clarity and fuller understanding of the invention, the firearm 10 will be hereinafter described as a gas-operated automatic rifle. The rifle 10 comprises a lower receiver 12 housing the lockwork of the rifle and an interconnected upper receiver 14 provided with a longitudinal cavity or chamber 16 in which reciprocates a bolt carrier assembly generally designated 18. Threadahly connected to the receiver is a receiver extension 20 housing a suitable recoil mechanism for the bolt carrier assembly 18. Immediately below chamber 16 and communicating therewith is a second or trigger chamber 22 located within the lower receiver 12 and housing the trigger mechanism generally designated 24, the mechanism 24 being similar in design and operation to the mechanism described in United States Patent No. 3,045,555 issued July 24, 1962, to E. M. Stoner. The trigger mechanism 24 includes, in addition to the trigger 26, the hammer 28 and the intermediate sear 30, a safety selector 32 which can be externally manipulated, by means not shown, to lock the rifle in a nonfiring safety position or to permit semiautomatic or automatic operation thereof.

When the safety selector 32 is in the automatic firing position, the cocked trigger mechanism will be positioned as illustrated by the phantom lines of FIG. 1. As more fully described in the aforementioned Stoner patent, the illustrated cocked nonfiring position of the hammer 28 is maintained bythe cooperative interengagement between the trigger sear 34 and the lower hammer notch 36, sear 34 being held in contact therewith under the bias of trigger spring 38. A rearward pull on the trigger 26 causes the clockwise pivoting thereof about the trigger pin 40 and results in the disengagement of trigger sear 34 from the notch 36. The hammer 28 is then free to rotate clockwise about its pivot pin 42 under the bias of the hammer spring 44 and strike the firing pin 46. The firing pin in turn actuates the cartridge thereby firing the rifle. The firing of the rifle causes the bolt carrier assembly 18 to recoil or move rearwardly within the chamber 16 under the influence of the gas pressure generated by the burning powder and to repeatedly and automatically cock the hammer, chamber a succeeding cartridge, and fire the rifle for as long as the trigger remains pulled.

In accordance with the present invention it is now possible to control the time lapse required for each firing cycle, as described above, and particularly to lengthen the cycle time of automatic operation thereby slowing down the firing rate of the rifle. The controlled time increase is provided by introducing a hesitation or delay into the hammeractuation upon return of the bolt carrier assembly 18 to a closed and locked battery position. The assembly 18 comprises an elongated sleevelike bolt carrier 48 having a generally cylindrical configuration and an axial bore 50 extended therethrough. Operatively supported within the axial bore 50 at the forward end thereof is a bolt, not shown, which mounts the firing pin 46 adjacent'a pair of longitudinally extending circumferentially spaced apertures 52, 54 in the periphery of the carrier 48. The apertures are arranged on the bottom and top respectively of the carrier 48 and are of suflicient width to permit the passage therethrough of the hammer 28 as it pivotally moves toward the firing pin under the bias of spring 44. The forward termination of bottom'aperture 52 adjacent firing pin 46 provides bolt carrier .48 with a shoulder 56 which acts against hammer 28 during recoil to pivot the latter in a counterclockwise direction against the bias of hammer spring 44. At the same time, the automatic sear 58 rotates counterclockwise about its pivot pin 60 under the bias of spring 62 thereby moving it into position for engaging the terminal hook 64 of the hammer 28 upon return of the carrier 48 to the closed and locked battery position.

As shown, the bottom aperture 52 is positioned adjacent the trigger mechanism when the carrier 48 is in the battery position and is of suflicient length so that the rearward termination thereof, designated by the numeral 66, remains out of contact with the automatic sear 58 at all times. The carrier 48 is further provided with an elongated aperture extension or keyway 68 of generally rectangular cross section extending rearwardly from 66 and communicatively connecting that portion of chamber 22 located rearwardly of sear 58 with the portion of bore 50 rearward of aperture 52. As shown in FIG. 1, however, the keyway 68 does not extend to the end of carrier 48.

Slidable axially within the bore 50 is a shuttle 70 whose movement is restricted rearwardly by the cap 72 of buffer assembly 74 and forwardly by the cross pin 76 mounted on carrier 48 in such a manner as to traverse bore 50 forwardly of aperture termination 66. The shuttle 70 consists of a solid cylindrical timing slug 78 and an integral bifurcated sear release 80 depending downwardly as a lower extension from the forward end of slug 78. The shuttle is arranged within bore 50 so that release 80 freely slides within the keyway 68.

As will be appreciated, during the automatic operation of the rifle the recoil movement of the carrier 48 not only pushes the hammer 28 downwardly causing hook 64 to become positioned under sear 58 but at the same time tends to press the shuttle 70 forwardly against cross pin 76 causing the shuttle to be carried rearwardly with the bolt carrier, the bifurcated sear release 80 readily passing over the buffer stop detent 82. As the carrier 48 is halted in its rearward movement by the action of the compression recoil spring, not shown, against the buffer assembly 74, the shuttle 70 tends to continue its rearward motion under its own momentum and slides rearwardly until it rests against the buffer cap 72. In fact, it is the coupled effect of the rearward inertia of the shuttle and the action of the recoil spring moving the carrier forwardly into the battery position that urges the shuttle into its rearwardmost position. Thus, as the bolt carrier moves forwardly into the closed battery position two forces tend to place the shuttle at the rear of the bolt carrier 48.

As the carrier 48 returns and the aperture 52 passes over the hammer 28, the latter will iiioveupwardly under the bias of hammer spring 44. However, the automatic sear 58 having rotated counterclockwise under the bias of spring 62 makes contact with the hook 64 of the hammer preventing the complete fall of the hammer. As illustrated by the full line portions of FIG. 1, the bolt carrier 48 will stop at the fully closed and locked battery position before the shuttle 78 moves 'out of its abutting relationship with the buffer assembly 74. However, at that time the hammer 28 has not yet been tripped since the elongated aperture 52 is of suflicient length to prevent contact between the carrier 48 and the automatic sear 58. The momentum of the shuttle 70 causes its continued forward travel beyond the full line position, as shown in FIG. 1, up to the phantom line -position. As the shuttle approaches the latter position its outwardly extending sear release portion 80 traveling within the keyway 68 contacts the sear 58 causing disengagement between the automatic sear and the terminal book 64 and permitting the fall of the hammer against the firing pin 46 under the bias of the hammer spring 44. The cycle will then be repeated so long as the trigger is held rearwardly preventing the interconnection between the trigger sear 34 and the lower notch 36 on the hammer.

Since the velocity of the bolt carrier is known, the time lapse for each cycle can be calculated for various axial travel distances as well as for timing slugs of different weight and composition. It will, of course, be appreciated that the added weight of the reciprocating shuttle, in itself would reduce the rate of fire of the rifle even though this weight were not permitted to move within the carrier. However, the weight of the carrier could be so reduced that after assembly of the shuttle the total weight may be the same as in a standard bolt carrier in which case the slowdown effect would be entirely caused by the axial travel of the shuttle. In this way the exact firing rate can be rather carefully controlled with a minimum of change in the rifle.

Referring now to FIGS. 2 and 3 there is shown a similar delay shuttle 84 possessing the integral bifurcated lower extension 86 which travels within the keyway 68 and acts in the same manner as extension 80 to effect release of the hammer during automatic operation of the rifle. The shuttle 84 employs a timing slug 88 provided with an axial bore 90 in which is positioned a timing converter 92. The converter 92 consists of a cylindrical rod 94 having at one end thereof an integral annular ring or disc 96 of greater diameter than the rod. The disc 96 fits within the counterbore portion 98 of bore and is held therein by the spring detent 100, shown in phantom. This arrangement permits the use of the rifle for either delay or normal automatic firing by merely reversibly positioning the timing converter 92 within the countorbore 98 of the timing slug 88. It will be appreciated that the timing converter 92 is of suflicient length so that in the position shown in FIG. 3 the rod 94 abuts the buffer cap 72 while the slug 88 fits snugly and relatively immovably against the cross pin 76, thereby causing extension 86 to trip the hammer immediately upon closing of the bolt carrier. Thus, by a reversal of the timing converter 92, the operator can adjust the automatic firing of the rifle in an extremely quick and facile manner from the delay firing rate to the normal firing rate depending upon the manner in which the parts are assembled.

Where a still longer delay or slower rate of fire is desired the device may be modified as shown in FIG. 4 to include a lightweight strip or lever 102 pivotally mounted within the axial bore 50 of the bolt carrier by means of pivot pin 104. The lever 102 hangs downwardly a suflicient distance so that the bifurcated free end thereof rests within the elongated keyway 106, the keyway, as shown, extending all the way to the rearward end of the bolt carrier. Excessive pivotal movement of the lever 102 is limited by a pair of cross pins 108, located within the bore of the bolt carrier 48. Forward cross pin 110 is located adjacent the rearward extremity of aperture 52 in a manner similar to cross pin 76 and acts solely as a pivot stop for lever 102. Cross pin 108 on the other hand is mounted rearwardly of lever 102 and acts not only as a pivot stop but also as a limit stop for shuttle 112. Thereby the cross pins act to ensure that the lever 102 is in a position to contact the automatic sear 58 when the strip is struck by the shuttle.

In the same manner as described hereinbefore the shuttle 112 is positioned within the bore 50 of the bolt carrier. The shuttle 112 includes a disc-like timing slug 114 having a bifurcated depending lower extension 116 which protrudes downwardly into the keyway 106 and forwardly a distance greater than the diameter of cross pin 108. Integrally connected to the rear surface of slug 114 and extending rearwardly therefrom is the cylindrical stabilizing rod 118 which passes through the central aperture 120 in the buffer cap 122 of the buffer assembly. Advantageously the rod 118 additionally provides the slug 114 with the added weight necessary to cause release of the automatic sear during its return travel.

The lightweight lever 102 is so fashioned and positioned that it contacts the automatic sear 58 when the bolt is closed and locked. However, due to the light weight of this component and the fact that the pivot pin 104 absorbs approximately one-half the energy of this component when the bolt carrier is arrested in its forward travel, the momentum thereof is insufiicient to disengage the automatic sear with the hook 64 of the hammer. The shuttle acts in the manner described hereinbefore yet provides a greater delay since it contains a smaller slug 114 and is arranged to project rearwardly into the buffer assembly while remaining free to slide along the bore 50. Upon forward movement it strikes the lightweight lever 102 near its lower extremity causing the automatic sear 58 to disengage the terminal hook 64 permitting the fall of the hammer.

As will be apparent from the foregoing description, the present invention provides relatively precise control over the firing rate of an automatic rifle by employing a bolt carrier assembly which includes means for incorporating a positive time lapse in the firing cycle between the final closing of the bolt carrier and the automatic release of the hammer. This delayed actuation of the hammer is accomplished without altering the lockwork of the rifle and without requiring substantial change in the remaining working mechanisms yet provides an effective control device which is entirely enclosed within the receiver of the rifle. Further, the delay control device is adapted for rapid assembly as well as rapid conversion from a normal to a delayed firing rate during automatic operation. Not insignificant is the fact that the present invention also effectuates these beneficial results without adversely or otherwise effecting the semiautomatic or single shot operation of the firearm.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure abovedescribed will become readily apparent without departure from the spirt and scope of the invention, the scope of which is defined in the appended claims.

I claim:

1. In an automatic firearm of the type wherein seating of the bolt and associated parts triggers the hammer fall of an immediately succeeding shot, the combination of. a firing rate control device comprising slidable intertia delay means temporarily immovable relative to said bolt immediately prior to said seating and movable subsequent to the seating of said bolt to release the hammer for triggering said hammer fall of a succeeding shot only during automatic operation of the firearm and at a positive time interval after said seating.

2. In an automatic firearm of the type wherein seating of the bolt carrier assembly triggers the hammer fall of an immediately succeeding shot, a firing rate control device comprising a slidable inertia delay member, said member being temporarily immovable relative to the bolt carrier assembly immediately prior to said seating while being actuatable by the seating of said assembly and movable subsequent thereto to release the hammer for triggering said hammer fall of a succeeding shot only during automatic operation of the firearm and at a positive time interval subsequent to said seating.

3. In an automatic firearm wherein a hammer repeatedly moves into a cocked position, a firing rate control device comprising a bolt carrier assembly movable into and out of a battery position, said assembly including slidable fire retarding means operable subsequent to seating of the assembly in the battery position to release the hammer of said firearm from the cocked position only during automatic firing and after a positive time lapse from said seating.

In an automatic firearm of the type wherein seating of the bolt carrier assembly triggers the hammer fall of a succeeding shot, a firing rate control device adapted to delay such triggering for a positive time interval comprising a bolt carrier movable into and out of a seated battery position, and a slidable inertia shuttle member immovable relative to said carrier during a substantial portion of said movement into and out of said seated position, said shutthe member being actuatable upon the rapid seating of said carrier and movable subsequent thereto to release the hammer for triggering said hammer fall of a succeeding shot only during automatic operation of the firearm and at a positive time interval after the seating.

5. In an automatic firearm of the type wherein seating of a bolt carrier assembly triggers the hammer fall of the next succeeding shot, the combination of a trigger mechanism and a firing rate control assembly mounted adjacent the trigger mechanism, said assembly comprising a bolt carrier adapted for movement into and out of a seated battery position and a slidable inertia fire retarding member mounted on the carrier and being immovable with respect thereto during a substantial portion of said movement, said carrier having an aperture of sufficient size to prevent contact between the carrier and the trigger mechanism for causing said hammer fall when the carrier is in the battery position, said fire retarding member being movable to release said hammer only during automatic operation thereof and after a positive time interval subsequent to the carrier being seated in the battery position.

6. In an automatic firearm the combination of a receiver; a trigger mechanism mounted in the receiver; and a firing rate control assembly movable within and entirely enclosed by the receiver, said delay assembly compris ing an elongated bolt carrier adapted for rapid reciprocal movement into and out of a battery position and having a shuttle slidably mounted thereon, said carrier having an axial bore through at least a portion thereof and a peripheral aperture intermediate the ends thereof communicating with said bore, said aperture being of sufficient size to preclude contact between the carrier and the trigger mechanism when the carrier is in the battery position, said shuttle including depending means adapted to actuate the firearm only during automatic operation thereof and after a given time interval subsequent to the carrier being seated in the battery position.

7. An automatic firearm as set forth in claim 6 wherein said shuttle is a generally cylindrical slug slidably retained within the axial bore of the carrier and said included depending means is an integral release member extending outwardly of said bore.

8. An automatic firearm as set forth in claim 7 wherein said cylindrical slug is provided with an axial aperture and a delay converting means mounted in said axial aperture.

9. An automatic firearm as set forth in claim 7 wherein said cylindrical slug is provided with an elongated rod extending rearwardly therefrom to adjacent the end of said carrier.

10. In an automatic firearm'the combination of a receiver, a trigger mechanism incluing a hammer, and a firing rate control assembly mounted entirely within the receiver adjacent the trigger mechanism, said assembly comprising a bolt carrier reciprocably movable into and out of a battery position and adapted to cock said hammer during such movement, said carrier having an axial bore through at least the rearward portion thereof and a peripheral aperture intermediate the ends thereof communicating with said bore, said aperture being of sufficient size to preclude contact between the carrier and the trigger mechanism when the carrier is in the battery position, said assembly including a shuttle mounted within said bore for limited slidable movement therealong, said assembly including trigger mechanism contacting means adapted to actuate the firearm only during automatic operation thereof and after a given time interval subsequent to the carrier being seated in the battery position, and means for limiting the slidable movement of said shuttle.

11. In a gas-operated firearm the combination of a receiver, a trigger mechanism mounted in the receiver and including a hammer and an automatic sear, and a firing rate control assembly movably mounted entirely within the receiver, said control assembly comprising a delay timing slug and a bolt carrier adapted for reciprocal movement between battery and retracted positions having an axial bore and a longitudinal aperture intermediate the ends thereof, said aperture being of sufiicient size to preclude contact between the trigger mechanism and the carrier when the carrier is in the battery position, said carrier further having a slotted keyway communicating with said aperture and extending rearwardly therefrom, said timing sl'ug being axially slidable within said bore between the rearward end thereof and said aperture and having an outwardly extending sear release positioned within the keyway, said release being adapted to actuate the fall of the hammer only during automatic operation of the firearm and after a given time lapse subsequent to the carrier being seated in the battery position.

12. A firearm as set forth in claim 11 wherein said timing slug is a generally cylindrical member having a diameter slightly less than the diameter of said bore.

13. A fireanin as set forth in claim 12 wherein said References Cited by the Examiner cylindrical slug is provided with an elongated rod extend- FOREIGN PATENTS ing rearwardly therefrom to adjacent the end of said ca -rim; 439,792 9/1948 Italy.

14. A firearm as set forth in claim 13 wherein said delay 5 297'450 6/1954 Switzerland assembly includes a lightweight plate pivotally mounted within the bore for effecting contact with the automatic BENJAMIN Pfimm'y Examinersear immediately upon movement of the carrier to the FRED MATTERN battery position, said plate being incapable of independ- Y ently actuating said sear. 10 S. C. BENTLEY, Assistant Examiner. 

1. IN AN AUTOMATIC FIREARM OF THE TYPE WHEREIN SEATING OF THE BOLT AND ASSOCIATED PARTS TRIGGERS THE HAMMER FALL OF AN IMMEDIATELY SUCCEEDING SHOT, THE COMBINATION OF A FIRING RATE CONTROL DEVICE COMPRISING SLIDABLE INTERTIA DELAY MEANS TEMPORARILY IMMOVABLE RELATIVE TO SAID BOLT IMMEDIATELY PRIOR TO SAID SEATING AND MOVABLE SUBSEQUENT TO THE SEATING OF SAID BOLT TO RELEASE THE HAMMER FOR TRIG- 